##M:Part Seat clamp mount 31.8 millimetre black The M:Part Seat clamp mount 31.8 millimetre black is a simple solution for those wanting to fit a rack to a bike that does not have rack mounts. For use with seat post that have a 31.8 millimetre internal diameter and smaller frames without rack braze-ons or wishbone rear stays. No ordinary clamp, the M:Part Seat clamp mount 31.8 millimetre black has bosses allowing a rear rack to be easily and securely fitted. This is a strong mount with stainless steel bolts and hardware and a black design.